Html Encode in ASP.NET Web Control

I have a file called TopicTree.ascx.cs which I am trying to output encoded strings like so:

            string subject = 开发者_如何学Creader.IsDBNull(0) ? string.Empty : reader.GetString(0);
            string topic = reader.IsDBNull(1) ? string.Empty : reader.GetString(1);

            subject = subject.Trim();
            topic = topic.Trim();

            string en_subject = Server.HtmlEncode(subject);
            string en_topic = Server.HtmlEncode(topic);

            string output = string.Format("<li><a href=\"searchresults.aspx?type=topics&subject={1}&topic={2}\" style=\"cursor: pointer;\">{0}</a></li>", topic, en_subject, en_topic);

But when I actually see the output on the screen, it isn't encoded. What's wrong?

For the link URL, you want Server.UrlEncode() instead of Server.HtmlEncode().

But for the link display, you want Server.HtmlEncode(topic) on the topic as well.